The principal modification was an increase of the interval between convoys, first, to four, and later to five days in order to relieve the strain on the Grand Fleet arising from the provision of covering forces; the disadvantage of the resultant increased size of the convoys had to be accepted.

Under the new system the Commander-in-Chief Coast of Scotland at Rosyth--Admiral Sir Cecil Burney--became responsible for the control of the Scandinavian convoys, the Admiralty selecting the routes.
The introduction of the convoy system for the Atlantic trade dates from the early days of May, 1917, when the prospect--for it was only then a prospect--of increasing assistance from the U.S.Navy in regard to destroyers and other small craft for escort duty as well as convoy cruisers for ocean work, made the system possible.

Action taken with the U.S.authorities for the introduction of a system by which the trade from that country in neutral shipping was controlled enabled the ships of the 10th Cruiser Squadron to be gradually withdrawn from blockade duties and utilized as ocean convoy cruisers.

Even with assistance from the U.S.Navy in the shape of old battleships and cruisers, the use of the 10th Cruiser Squadron, the withdrawal of the 2nd Cruiser Squadron of five ships from the Grand Fleet, the use of the ships of the North American and West Indies Squadron and of some of our older battleships from the Mediterranean, there was still a shortage of convoy cruisers; this deficiency was made up by arming a number of the faster cargo vessels with 6-inch guns for duty as convoy cruisers.

These vessels usually carried cargo themselves, so that no great loss of tonnage was involved.
On May 17 a committee was assembled at the Admiralty to draw up a complete organization for a general convoy system.